2.3. Analytical method Samples were analyzed with ultrahigh performance liquid chro-matography (UHPLC) coupled to a quadrupole time of flight (QToF)mass spectrometer (Acquity QToF Premier system; Waters, Man-chester, UK) using electrospray ionization (ESI). Separation wasachieved by an HSS T3 column (100 mm × 2.1 mm, particle diam-eter 1.8 m; Waters) and a binary gradient. The mobile phaseconsisted of (A) H2O:ACN (95:5, v:v) and (B) ACN:H2O (95:5, v:v),respectively, both containing 10 mM of HAc. The UHPLC was pro-grammed to deliver a linear gradient from 100% A to 95% B in 5 min,followed by 5 min of 95% B, at a constant flow rate of 0.3 mL min−1.The QToF-MS was operated in full scan mode at a mass resolution of approximately 8000. Each sample was analyzed in positive andnegative ionization mode in two separate runs. To obtain additional structural information, two acquisition functions were concur-rently acquired in MSE mode, at low (2 eV) and high collision energy(20 eV). A methanolic sulfadimethoxine solution (100 ng mL−1) was introduced every 5 s through the LockSpray probe at a flow rate of20 L min−1 to compensate for mass drifts.)